Mobile communication devices, such as mobile telephone handsets, tablet based computers, laptop computers, and other electronic devices provide various functions to users such as telephone calling, emailing, surfing the World Wide Web, composing and sending text messages, interacting with mobile applications, and other functionality. Mobile communication devices may incorporate one or more antennas. These antennas generally radiate radio frequency (RF) energy to transmit information. In some instances, a human body may be exposed to this radiated RF energy, e.g., when a person talks on a mobile telephone handset.
Specific absorption rate (SAR) is a measure of the rate at which energy is absorbed by, for example, the human body, when exposed to a RF electromagnetic field, e.g., from a mobile communication device.
Mobile communication devices may be subject to SAR limits, e.g., limits on the rate at which energy will be absorbed by the human body when exposed to radiated RF energy from the mobile communication device. In many countries, to ensure that users of mobile communication devices are not exposed to unacceptable radiation levels, limits are placed on SAR. For example, the Federal Communications Commission (FCC) has SAR limits (FCC limits) in place in an effort to ensure that mobile communication device users are not exposed to unacceptable radiation levels.
Thus, one obstacle faced by mobile communication device manufacturers is to meet the SAR regulatory requirements for the particular country or countries where the mobile communication devices will be used.
Compliance with SAR limits might be achieved by fixing maximum RF transmit power for a mobile communication device to a power level that maintains legal compliance. Limiting transmit power, however, may underutilizes the capabilities of the mobile communication device and may adversely impact communication connections, communication quality, or both.
Compliance with SAR limits might also be achieved by adding additionally hardware, such as shielding to filter out any RF emissions that exceed SAR limits. Added hardware, such as added shielding to filter out RF emissions that exceed SAR limits, may add additional hardware to the antenna, extra weight due to the added hardware, or added cost for the hardware added to the antenna or antennas. Additionally, the use of shielding generally wastes energy because energy that could be transmitted is now blocked by the shield. Thus, the use of shielding may be less efficient and may impact over the air performance.